Core Practical 10 Lab

Aims

To construct an electrochemical cell

To measure the electrode potential of a selection of electrochemical cells

Equipment

● 50 cm3 of 0.4 mol dm−3 zinc sulfate solution ● 50 cm3 of 0.4 mol dm−3 copper(II) sulfate solution ● 50 cm3 of 1.0 mol dm−3 iron(II) sulfate solution ● 50 cm3 of 0.1 mol dm−3 silver nitrate solution ● saturated potassium nitrate solution ● distilled/deionised water ● one strip of each of the following: zinc; copper; iron and silver ● sandpaper ● four 100 cm3 beakers ● strips of filter paper about 12 cm long ● 100 cm3 measuring cylinder ● voltmeter (20 V) reading to 2 d.p. ● connecting wires and crocodile clips

1. Clean the strips of zinc and copper using sandpaper.

2. Set up a zinc half-cell by pouring 50 cm3 of zinc sulfate solution into a 100 cm3 beaker and standing the strip of zinc in the beaker.

3. Set up a copper half-cell by pouring 50 cm3 of copper(II) sulfate solution into a separate 100 cm3 beaker and standing the strip of copper in the beaker.

4. Make an electrical connection between the two beakers by joining them with a strip of filter paper that has been dipped in a saturated solution of potassium nitrate (this acts as a salt bridge), as shown in the diagram.

5. Join the two metal strips with a voltmeter, using the connecting wires and crocodile clips.

6. Record the electrode potential of the [Zn(s) | Zn2+(aq)] and [Cu2+(aq) | Cu(s)] system. If the voltmeter gives a negative value, reverse the connections so that it gives a positive value.

7. Now, repeat steps 1–6 using the following combinations of metal/metal ion half-cells. Remember to clean the metal strips with sandpaper before use.

[Zn(s) | Zn2+(aq)] and [Fe2+(aq) | Fe(s)]

[Fe(s) | Fe2+(aq)] and [Cu2+(aq) | Cu(s)]

[Zn(s) | Zn2+(aq)] and [Ag+ (aq) | Ag(s)]

[Cu(s) | Cu2+(aq)] and [Ag+ (aq) | Ag(s)]